This invention relates to elastic prophylactic sheaths, such as those used as gloves, condoms, finger cots and the like. In particular, this invention relates to elastomeric polymer sheaths and the augmented borders at the open ends of these sheaths, which facilitate the placement of the sheaths over the body members on which they are used as well as their removal after use.
The use of prophylactic sheaths is continually broadening in both clinical and consumer applications. The sheath most commonly known to the consumer is the condom, with world-wide use in a wide range of civilizations and cultures, for both contraception and prevention of the transmission of sexually transmitted disease. The most common material form which condoms and other prophylactic sheaths are fabricated is latex.
Certain classes of elastomeric polymers offer advantages over latex as materials for prophylactic sheaths. Polyurethane, for example, has both a strength and a tensile modulus approximately three times those of latex. Similar properties are found in other thermoplastic elastomers, particularly block copolymers formed by combining hard and soft segments of appropriate structure in proportions and arrangements selected to provide the resulting copolymer with the desired properties. The selection of the particular segments as well as their proportions and arrangements in the block copolymer are within the knowledge of those skilled in the copolymer art.
The advantage of the use of such materials is that they can be used to form sheaths of less than half the thickness of the latex products but with equivalent strength. With such a reduced thickness, these products provide greater transmission of heat and sensation.
Specific classes of elastomeric polymers offer further advantages due to their chemical structure. Polyurethanes, for example, tend to soften in a warm, moist environment. They are also easier to sterilize and more biocompatible than latex (less tendency to cause allergic reactions), are odorless and tasteless, and have a longer shelf life. Further, there are no limitations on the types of lubricant which can be used with polyurethanes--they are inert, for example, to oil-based lubricants such as petroleum jelly.
The availability of polyurethanes and other high strength elastomers permits one to form sheaths of extraordinary thinness without compromising on the strength of the material or its ability to resist pinhole formation. These materials lack however a high degree of elasticity, and as a result are somewhat difficult to place over the body member for use, particularly when this is done by unrolling the sheath over the member. In the case of condoms, border rings are generally incorporated into the condom structure to facilitate the unrolling. Without such rings, the condom would be difficult to grasp and would lack the bulk needed to permit it to be unrolled. It would also have a tendency to roll back on itself.
These border rings are generally made of the same material as the condom, however, with high strength materials, considerable force is required to stretch the ring enough to position the condom as well as unroll it. This is particularly true when the circumference of the body member is larger than the diameter of the rolled condom. The result is discomfort to the user as well as a risk of tearing the condom during application. Similar problems, although less critical, are encountered during removal of the condom (as well as other types of prophylactic sheaths) after use.